The invention relates to an apparatus for automatically soldering jewelry chains, especially flexible neck chains, to special chain parts such as locks or pieces of jewelry.
For proper soldering operation, it is important that the chain ends and the jewelry pieces or other pieces to be soldered to the chain ends are held in proper positions relative to one another. In order to be able to hold the end pieces properly by means of grippers, it is necessary that the end links of the chain are previously properly formed by a corresponding cutting step. Generally, a link is to be cut exactly in the middle of its length. If the end link does not have the shape required for gripping or if, during the cutting process, two chain links are cut, the grippers cannot properly hold the end link, that is, it cannot bring the end link into proper position with respect to the counterpiece to which it is to be soldered so that improper, usually unusable, soldering joints are produced. It any case, disturbances in the production process will result.
It is pointed out that for jewelry chains, tensile strength is not of prime importance, it is rather the attractive appearance of the chain which is achieved by various shaping of the chain links. Such shaping of the chain links results in a relatively low longitudinal stability of the chain since only relatively small tension forces may deform the links and lengthen the chain, resulting in a reduction of chain links per length unit. The assumption of a given chain or link length in connection with the design of a cutting apparatus will therefore not lead to the desired result since, on this basis, there is no assurance that a chain link will indeed be cut exactly in the middle.
For a proper operation of an automatic soldering apparatus it is therefore necessary that the end link of a chain is properly held and also, that the link is subsequently properly cut, generally in the middle of the chain link engaged by the apparatus. However, with prior art apparatus neither could be done with the degree of certainty necessary for the manufacture; it was more or less accidental where the grippers engaged the chain and exactly where it was cut. As a result such automatic apparatus could properly handle only inflexible chains which are easier to position and for which the shape of the joint pieces is not as critical as it is with flexible chains. Flexible chains are therefore soldered generally manually with a high reject rate and at relatively high costs.
In order to be able to use automatic soldering apparatus also with flexible chains it has been tried to engage not just one link but a number of somewhat remote links (DE-OS No. 33 02 208, GB-A No. 2084906 and GB-A No. 2115321) to hold and guide the chain in this manner toward the member to be soldered thereto. In this case, the last link to be soldered is not firmly engaged. Actually, it is impossible to engage the last link since the cutting of the chain is random so that the end link is of different shape with each cut, that is, the cut edges of the link are anywhere around the outline of the link. There are many possibilities for the location of the cutting plane depending on the accidental position of the chain end upon cutting which results in different soldering connections and different shapes of the soldered chain ends, many of which are not acceptable by appearance or quality standards.